Technical Field
The present invention relates to a premix gas burner for operation in blue flame mode that is having a burner deck comprising a fiber based substrate and a screen or perforated plate supporting the fiber based substrate. The premix gas burner is further comprising contact wires forming a thermocouple fixed to the burner deck.
Background Art
Premix gas burner with operation in blue flame mode are known. The gas premix is burnt on a burner substrate and blue coloured flames are visible. The flue gas is containing the caloric value and will transfer its energy onto another medium, e.g. through a heat exchanger to water in a water heater. A different type of burners are radiation burners that operate in red flame mode to transfer their energy via radiation. Both types of burners (for operation in blue flame mode or for operation in red flame mode) are different in construction in order to be optimized for their mode of operation.
One way to control the combustion of a premix gas burner for operation in blue flame mode makes use of a measurement of a temperature at or on the burner deck.
GB 2 270 748 discloses a gas burner that is provided with a thermocouple for sensing the temperature of the surface of the burner, the burner deck may have a metallic perforated plate or a ceramic burner. The thermocouple is fixed to the underside (=non-combustion side) of the burner deck.
EP 1 039 220 discloses a premix gas burner that is having a perforated plate diffuser to which one or more thermocouples are attached.
EP 2 180 253 is describing prior art in which thermocouples are welded to the inner (=gas supply) side or outer (=combustion) side of a burner. Furthermore, EP 2 180 253 is disclosing a temperature sensor for a gas premix burner. The temperature sensor comprises two metal wires implementing a thermocouple, a protection sheath receiving the two metal wires, and a head in metal material having a front side intended to be facing the environment, the temperature of which is intended to be measured, and a rear side opposite the front side, in which the two metal wires are connected in a thermal exchange relationship to the head rear side, and the head comprises a front portion connectable to a burner wall of the burner so that the thermocouple is connectable to the burner by means of said metal head. The temperature sensor is used for gas premix burners having a perforated plate as burner deck.
It is a problem of the temperature measurement systems as known in the art (as described in GB 2 270 748, EP 1 039 220, in the prior art part as well as in the disclosing part of EP 2 180 253) that these temperature measurement systems do not result in reliable temperature results when a fiber based substrate supported by a screen or by a perforated plate is used as burner deck in gas premix burners.